During the Circumpolar Flaw Lead (CFL) System Study, 17 stations were sampled in the Amundsen Gulf (Western Arctic), a very dynamic area with heterogeneous ice conditions. In order to track metabolic diversity of heterotrophic bacterioplankton, Biolog MT2 MicroPlates® amended with custom selected substrates were inoculated with seawater from ice-covered to icefree conditions. Samples were taken from February to July 2008 at the surface (0-12 m) and intermediate depths (20-70 m). In winter, when concentrations of nutrients and chlorophyll a were extremely low, the number of substrates used was close to zero. In early spring, when the levels of chlorophyll a increased, so did the number of substrates used. This was followed by a onemonth period with no substrates used in April and May. Finally, the activity recovered towards the summer. The group of substrates most commonly used at all depths was carbohydrates, specially glucose and cellobiose. Amino acids were occasionally used both in surface waters and at intermediate depths. L-threonine was the most commonly used amino acid, together with Larginine and L-lysine at the surface and L-leucine at intermediate depths. These results were compared to those of a previous study in Franklin Bay, a relatively close area but with a different ice regime, showing a stable layer of land-fast ice throughout the period of study. The differences found in the metabolic capabilities between the two studies were likely a consequence of the different hydrography